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Thermodynamics Table of Contents Section 1 Relationships Between Heat and Work Section 2 The First Law of Thermodynamics Section 3 The Second Law of Thermodynamics

Section 1 Relationships Between Heat and Work
Chapter 10 Objectives Recognize that a system can absorb or release energy as heat in order for work to be done on or by the system and that work done on or by a system can result in the transfer of energy as heat. Compute the amount of work done during a thermodynamic process. Distinguish between isovolumetric, isothermal, and adiabatic thermodynamic processes.

Heat, Work, and Internal Energy
Section 1 Relationships Between Heat and Work Chapter 10 Heat, Work, and Internal Energy Heat and work are energy transferred to or from a system. An object never has “heat” or “work” in it; it has only internal energy. A system is a set of particles or interacting components considered to be a distinct physical entity for the purpose of study. The environment the combination of conditions and influences outside a system that affect the behavior of the system.

Heat, Work, and Internal Energy, continued
Section 1 Relationships Between Heat and Work Chapter 10 Heat, Work, and Internal Energy, continued In thermodynamic systems, work is defined in terms of pressure and volume change. This definition assumes that P is constant.

Heat, Work, and Internal Energy, continued
Section 1 Relationships Between Heat and Work Chapter 10 Heat, Work, and Internal Energy, continued If the gas expands, as shown in the figure, DV is positive, and the work done by the gas on the piston is positive. If the gas is compressed, DV is negative, and the work done by the gas on the piston is negative. (In other words, the piston does work on the gas.)

Heat, Work, and Internal Energy, continued
Section 1 Relationships Between Heat and Work Chapter 10 Heat, Work, and Internal Energy, continued When the gas volume remains constant, there is no displacement and no work is done on or by the system. Although the pressure can change during a process, work is done only if the volume changes. A situation in which pressure increases and volume remains constant is comparable to one in which a force does not displace a mass even as the force is increased. Work is not done in either situation.

Thermodynamic Processes
Section 1 Relationships Between Heat and Work Chapter 10 Thermodynamic Processes An isovolumetric process is a thermodynamic process that takes place at constant volume so that no work is done on or by the system. An isothermal process is a thermodynamic process that takes place at constant temperature. An adiabatic process is a thermodynamic process during which no energy is transferred to or from the system as heat.

Thermodynamic Processes
Section 1 Relationships Between Heat and Work Chapter 10 Thermodynamic Processes Click below to watch the Visual Concept. Visual Concept

Section 2 The First Law of Thermodynamics
Chapter 10 Objectives Illustrate how the first law of thermodynamics is a statement of energy conservation. Calculate heat, work, and the change in internal energy by applying the first law of thermodynamics. Apply the first law of thermodynamics to describe cyclic processes.

Chapter 10 Energy Conservation
Section 2 The First Law of Thermodynamics Chapter 10 Energy Conservation If friction is taken into account, mechanical energy is not conserved. Consider the example of a roller coaster: A steady decrease in the car’s total mechanical energy occurs because of work being done against the friction between the car’s axles and its bearings and between the car’s wheels and the coaster track. If the internal energy for the roller coaster (the system) and the energy dissipated to the surrounding air (the environment) are taken into account, then the total energy will be constant.

Chapter 10 Energy Conservation
Section 2 The First Law of Thermodynamics Chapter 10 Energy Conservation Click below to watch the Visual Concept. Visual Concept

Chapter 10 Energy Conservation
Section 2 The First Law of Thermodynamics Chapter 10 Energy Conservation

Energy Conservation, continued
Section 2 The First Law of Thermodynamics Chapter 10 Energy Conservation, continued The principle of energy conservation that takes into account a system’s internal energy as well as work and heat is called the first law of thermodynamics. The first law of thermodynamics can be expressed mathematically as follows: U = Q – W Change in system’s internal energy = energy transferred to or from system as heat – energy transferred to or from system as work

Signs of Q and W for a system
Section 2 The First Law of Thermodynamics Chapter 10 Signs of Q and W for a system

Chapter 10 Sample Problem The First Law of Thermodynamics
Section 2 The First Law of Thermodynamics Chapter 10 Sample Problem The First Law of Thermodynamics A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed from the refrigerant as heat?

Sample Problem, continued
Section 2 The First Law of Thermodynamics Chapter 10 Sample Problem, continued 1. Define Given: W = –135 J U = 114 J Diagram: Tip: Work is done on the gas, so work (W) has a negative value. The internal energy increases during the process, so the change in internal energy (U) has a positive value. Unknown: Q = ?

Sample Problem, continued
Section 2 The First Law of Thermodynamics Chapter 10 Sample Problem, continued 2. Plan Choose an equation or situation: Apply the first law of thermodynamics using the values for U and W in order to find the value for Q. U = Q – W Rearrange the equation to isolate the unknown: Q = U + W

Sample Problem, continued
Section 2 The First Law of Thermodynamics Chapter 10 Sample Problem, continued 3. Calculate Substitute the values into the equation and solve: Q = 114 J + (–135 J) Q = –21 J Tip: The sign for the value of Q is negative. This indicates that energy is transferred as heat from the refrigerant.

Sample Problem, continued
Section 2 The First Law of Thermodynamics Chapter 10 Sample Problem, continued 4. Evaluate Although the internal energy of the refrigerant increases under compression, more energy is added as work than can be accounted for by the increase in the internal energy. This energy is removed from the gas as heat, as indicated by the minus sign preceding the value for Q.

First Law of Thermodynamics for Special Processes
Section 2 The First Law of Thermodynamics Chapter 10 First Law of Thermodynamics for Special Processes Click below to watch the Visual Concept. Visual Concept

Chapter 10 Cyclic Processes
Section 2 The First Law of Thermodynamics Chapter 10 Cyclic Processes A cyclic process is a thermodynamic process in which a system returns to the same conditions under which it started. Examples include heat engines and refrigerators. In a cyclic process, the final and initial values of internal energy are the same, and the change in internal energy is zero. Unet = 0 and Qnet = Wnet

Cyclic Processes, continued
Section 2 The First Law of Thermodynamics Chapter 10 Cyclic Processes, continued A heat engine uses heat to do mechanical work. A heat engine is able to do work (b) by transferring energy from a high-temperature substance (the boiler) at Th (a) to a substance at a lower temperature (the air around the engine) at Tc (c). The internal-combustion engine found in most vehicles is an example of a heat engine.

Chapter 10 Combustion Engines
Section 2 The First Law of Thermodynamics Chapter 10 Combustion Engines Click below to watch the Visual Concept. Visual Concept

The Steps of a Gasoline Engine Cycle
Section 2 The First Law of Thermodynamics Chapter 10 The Steps of a Gasoline Engine Cycle

Chapter 10 Refrigeration Section 2 The First Law of Thermodynamics
Click below to watch the Visual Concept. Visual Concept

The Steps of a Refrigeration Cycle
Section 2 The First Law of Thermodynamics Chapter 10 The Steps of a Refrigeration Cycle

Thermodynamics of a Refrigerator
Section 2 The First Law of Thermodynamics Chapter 10 Thermodynamics of a Refrigerator

Section 3 The Second Law of Thermodynamics
Chapter 10 Objectives Recognize why the second law of thermodynamics requires two bodies at different temperatures for work to be done. Calculate the efficiency of a heat engine. Relate the disorder of a system to its ability to do work or transfer energy as heat.

Efficiency of Heat Engines
Section 3 The Second Law of Thermodynamics Chapter 10 Efficiency of Heat Engines The second law of thermodynamics can be stated as follows: No cyclic process that converts heat entirely into work is possible. As seen in the last section, Wnet = Qnet = Qh – Qc. According to the second law of thermodynamics, W can never be equal to Qh in a cyclic process. In other words, some energy must always be transferred as heat to the system’s surroundings (Qc > 0).

Efficiency of Heat Engines, continued
Section 3 The Second Law of Thermodynamics Chapter 10 Efficiency of Heat Engines, continued A measure of how well an engine operates is given by the engine’s efficiency (eff ). In general, efficiency is a measure of the useful energy taken out of a process relative to the total energy that is put into the process. Note that efficiency is a unitless quantity. Because of the second law of thermodynamics, the efficiency of a real engine is always less than 1.

Chapter 10 Sample Problem Heat-Engine Efficiency
Section 3 The Second Law of Thermodynamics Chapter 10 Sample Problem Heat-Engine Efficiency Find the efficiency of a gasoline engine that, during one cycle, receives 204 J of energy from combustion and loses 153 J as heat to the exhaust. 1. Define Given: Diagram: Qh = 204 J Qc = 153 J Unknown eff = ?

Sample Problem, continued
Section 3 The Second Law of Thermodynamics Chapter 10 Sample Problem, continued 2. Plan Choose an equation or situation: The efficiency of a heat engine is the ratio of the work done by the engine to the energy transferred to it as heat.

Sample Problem, continued
Section 3 The Second Law of Thermodynamics Chapter 10 Sample Problem, continued 3. Calculate Substitute the values into the equation and solve: 4. Evaluate Only 25 percent of the energy added as heat is used by the engine to do work. As expected, the efficiency is less than 1.0.

Section 3 The Second Law of Thermodynamics
Chapter 10 Entropy In thermodynamics, a system left to itself tends to go from a state with a very ordered set of energies to one in which there is less order. The measure of a system’s disorder or randomness is called the entropy of the system. The greater the entropy of a system is, the greater the system’s disorder. The greater probability of a disordered arrangement indicates that an ordered system is likely to become disordered. Put another way, the entropy of a system tends to increase.

Chapter 10 Entropy, continued
Section 3 The Second Law of Thermodynamics Chapter 10 Entropy, continued Greater disorder means there is less energy to do work. If all gas particles moved toward the piston, all of the internal energy could be used to do work. This extremely well ordered system is highly improbable.

Chapter 10 Entropy, continued
Section 3 The Second Law of Thermodynamics Chapter 10 Entropy, continued Because of the connection between a system’s entropy, its ability to do work, and the direction of energy transfer, the second law of thermodynamics can also be expressed in terms of entropy change: The entropy of the universe increases in all natural processes. Entropy can decrease for parts of systems, provided this decrease is offset by a greater increase in entropy elsewhere in the universe.

Energy Changes Produced by a Refrigerator Freezing Water
Section 3 The Second Law of Thermodynamics Chapter 10 Energy Changes Produced by a Refrigerator Freezing Water Because of the refrigerator’s less-than-perfect efficiency, the entropy of the outside air molecules increases more than the entropy of the freezing water decreases.

Entropy of the Universe
Section 3 The Second Law of Thermodynamics Chapter 10 Entropy of the Universe Click below to watch the Visual Concept. Visual Concept

Chapter 10 Multiple Choice
Standardized Test Prep Multiple Choice 1. If there is no change in the internal energy of a gas, even though energy is transferred to the gas as heat and work, what is the thermodynamic process that the gas undergoes called? A. adiabatic B. isothermal C. isovolumetric D. isobaric

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued 2. To calculate the efficiency of a heat engine, which thermodynamic property does not need to be known? F. the energy transferred as heat to the engine G. the energy transferred as heat from the engine H. the change in the internal energy of the engine J. the work done by the engine

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued 3. In which of the following processes is no work done? A. Water is boiled in a pressure cooker. B. A refrigerator is used to freeze water. C. An automobile engine operates for several minutes. D. A tire is inflated with an air pump.

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued 4. A thermodynamic process occurs in which the entropy of a system decreases. From the second law of thermodynamics, what can you conclude about the entropy change of the environment? F. The entropy of the environment decreases. G. The entropy of the environment increases. H. The entropy of the environment remains unchanged. J. There is not enough information to state what happens to the environment’s entropy.

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. 5. Which of the figures describes a situation in which U < 0, Q < 0, and W = 0? A. (a) B. (b) C. (c) D. (d)

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. 6. Which of the figures describes a situation in which U > 0, Q = 0, and W < 0? F. (a) G. (b) H. (c) J. (d)

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. 7. Which of the figures describes a situation in which U < 0, Q = 0, and W > 0? A. (a) B. (b) C. (c) D. (d)

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued Use the passage and diagrams to answer questions 5–8. A system consists of steam within the confines of a steam engine, whose cylinder and piston are shown in the figures below. 8. Which of the figures describes a situation in which U > 0, Q > 0, and W = 0? F. (a) G. (b) H. (c) J. (d)

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued 9. A power plant has a power output of 1055 MW and operates with an efficiency of Excess energy is carried away as heat from the plant to a nearby river. How much energy is transferred away from the power plant as heat? A  109 J/s B  109 J/s C  109 J/s D  109 J/s

Multiple Choice, continued
Chapter 10 Standardized Test Prep Multiple Choice, continued 10. How much work must be done by air pumped into a tire if the tire’s volume increases from m3 to m3 and the net, constant pressure of the air is kPa? F. 3.0  102 J G. 3.0  103 J H. 3.0  104 J J. 3.0  105 J

Chapter 10 Short Response
Standardized Test Prep Short Response Use the passage below to answer questions 11–12. An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room. 11. Does passing air through the air conditioner affect the temperature of the room? (Ignore the thermal effects of the motor running the compressor.)

Short Response, continued
Chapter 10 Standardized Test Prep Short Response, continued Use the passage below to answer questions 11–12. An air conditioner is left running on a table in the middle of the room, so none of the air that passes through the air conditioner is transferred to outside the room. 12. Taking the compressor motor into account, what would happen to the temperature of the room?

Short Response, continued
Chapter 10 Standardized Test Prep Short Response, continued 13. If 1600 J of energy are transferred as heat to an engine and 1200 J are transferred as heat away from the engine to the surrounding air, what is the efficiency of the engine?

Chapter 10 Extended Response
Standardized Test Prep Extended Response 14. How do the temperature of combustion and the temperatures of coolant and exhaust affect the efficiency of automobile engines?

Extended Response, continued
Chapter 10 Standardized Test Prep Extended Response, continued Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  105 J of energy as heat for the steam shovel to lift the dirt. 15. How much work is done by the steam shovel in lifting the dirt?

Extended Response, continued
Chapter 10 Standardized Test Prep Extended Response, continued Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  105 J of energy as heat for the steam shovel to lift the dirt. 16. What is the efficiency of the steam shovel?

Extended Response, continued
Chapter 10 Standardized Test Prep Extended Response, continued Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  105 J of energy as heat for the steam shovel to lift the dirt. 17. Assuming there is no change in the internal energy of the steam shovel’s engine, how much energy is given up by the shovel as waste heat?

Extended Response, continued
Chapter 10 Standardized Test Prep Extended Response, continued Use the information below to answer questions 15–18. In each problem, show all of your work. A steam shovel raises kg of dirt a vertical distance of 8.6 m. The steam shovel’s engine provides 2.00  105 J of energy as heat for the steam shovel to lift the dirt. 18. Suppose the internal energy of the steam shovel’s engine increases by 5.0  103 J. How much energy is given up now as waste heat?

Extended Response, continued
Chapter 10 Standardized Test Prep Extended Response, continued 19. One way to look at heat and work is to think of energy transferred as heat as a “disorganized” form of energy and energy transferred as work as an “organized” form. Use this interpretation to show that the increased order obtained by freezing water is less than the total disorder that results from the freezer used to form the ice.

Section 3 The Second Law of Thermodynamics
Chapter 10 Entropy

Energy Changes Produced by a Refrigerator Freezing Water
Section 3 The Second Law of Thermodynamics Chapter 10 Energy Changes Produced by a Refrigerator Freezing Water